129Xe nuclear magnetic resonance investigation of carbon black aggregate morphology

The morphology of three 'normal' ASTM carbon black reinforcement fillers (N110, N347, and N472) is investigated for the first time using one- and two-dimensional Xe-129 nuclear magnetic resonance (NMR) spectroscopy. A wide range in Xe-129 NMR chemical shift is observed among samples, and is attributed to variations in the physical nature of the unoccupied volume formed by the subunit particles of the aggregate. 129Xe NMR chemical shift and integrated intensity parameters are extracted from a single one-dimensional experiment, and interpreted in terms of aggregate void size, volume, and density. The rate of exchange of Xe-129 atoms between different aggregates in a three component blend is approximated using two-dimensional exchange NMR spectroscopy, and found to occur on a timescale similar to 6 ms less than or equal to tau(ex)less than or equal to similar to 100 ms. No evidence of xenon exchange between samples N110 and N472 was observed on timescales less than 100 ms, an apparent consequence of the small aggregate void size in these samples. The 129Xe NMR chemical shift assignments for samples N110, N347, and N472 are shown to be not significantly shifted from their non-exchanging values. (C) 1999 Elsevier Science Ltd. All rights reserved.